1. Field of the Invention
The present invention relates to a magnetic detection element that detects an external magnetic field, and more particularly to a magnetic impedance element (hereinafter referred to as xe2x80x9cMI elementxe2x80x9d) in which when a high-frequency current is supplied to an element body formed of a magnetic thin film, an impedance between both ends of the element body changes in accordance with an external magnetic field.
2. Related Background Art
In recent years, a magnetic detection element smaller in size and higher in sensitivity has been demanded as an information terminal device, a robot and so on using the magnetic detection element has been progressed. As the general detection element, there is a magneto resistancive element (hereinafter referred to as xe2x80x9cMR elementxe2x80x9d). As the sensitivity of the MR element, a rate of change in the resistance according to the external magnetic field is about 3%, and the magnetic field detection sensitivity by only the MR element is to the degree that the presence/absence of the geomagnetism can be detected. In the recent MR elements, there has been developed a GMR element (giant magneto resistive element) large in the rate of change in the resistance. However, even in the GMR element, when the rate of change in the resistance is about 10%, although the magnetic field detection sensitivity per se is improved to about several times, the sensitivity cannot be enhanced extraordinarily.
Under the above circumstance, the present inventors have already proposed an MI element in which when a high-frequency current is supplied to an element body formed of a magnetic thin film, an impedance between both ends of the element body largely changes in accordance with an external magnetic field (U.S. Pat. No. 5,764,055). The MI element of this type is that the magnetic thin film of the element body is so structured as to change the permeability with respect to the external magnetic field, and the skin effect by supply of the high-frequency current is changed, to thereby change the impedance.
FIG. 10 shows an example of an MI element using a conventional magnetic thin film. In this example, a magnetic thin film 110 of the element body is formed on a glass substrate 112 in a slender zigzag pattern obtained by folding a straight line in parallel several times. A direction of magnetic field detection is directed to a longitudinal direction of the pattern of the magnetic thin film indicated by an arrow in the figure. An easy axis of magnetization of the magnetic thin film 110 is so set as to be directed along the widthwise direction of the zigzag pattern. Upon supply of a high-frequency current of MHz orders by electrodes 114a and 114b at both ends of the pattern of the magnetic thin film 110, an impedance between the electrodes 114a and 114b changes in accordance with the external magnetic field.
The magnetic impedance characteristic with respect to the external magnetic field is shown in FIG. 11, in which the impedance changes in the form of V when the external magnetic field is within about xc2x15 oersted. The sensitivity is extremely high at an inclined portion of the V-shape of the characteristic, where the sensitivity of several tens to several hundreds of the MR element is obtained. However, because the magnetic field detection range excellent in linearity is only about 3 oersted, it is limited to the application of a magnetic sensor narrow in the detection range.
The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide an MI element in which an element body is formed of a magnetic thin film, (1) which is higher in the magnetic field detection sensitivity than an MR element and a GMR element, (2) which can take the same magnetic field detection range as that of a conventional MR element, and (3) which can obtain a stable sensitivity with a small element size (2 mm or less which is used as at least chip parts).
In order to solve the above problem, according to a first embodiment of the present invention, there is provided an MI element in which an element body is formed of a magnetic thin film formed on a non-magnetic substrate, and when a high-frequency current is supplied to said magnetic thin film, an impedance between both ends of said magnetic thin film changes in accordance with an external magnetic field, wherein said magnetic thin film is formed in a slender zigzag pattern obtained by folding a straight line in parallel several times, and an easy axis of magnetization of said magnetic thin film is so set as to be directed along the longitudinal direction of said pattern.
Also, according to the present invention, there is provided an MI element, wherein assuming that a thickness of said magnetic thin film is T, a line width of said pattern is W, and a length of said pattern is L, T is in a range of 1 to 5 xcexcm, and L/(Wxc3x97T) is in a range of 10 to 400xc3x97106 mxe2x88x921.
Other objects and features of the present invention will become apparent from the detailed description of the present invention with reference to the accompanying drawings.